2.6 Meiosis Flashcards
What sort of division does meiosis involve?
A reduction division
What is a reduction division?
Cells have full number of chromosomes to start but the cells formed have half the number
What is the name for a cell with half the number of chromosomes?
Haploid cell
Why are the cells made genetically different?
Because each ends up with a different arrangement of chromosomes
How many divisions occur in meiosis?
2
What are the stages of the first mitotic division?
Interphase 1 Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Cytokinesis
What occurs in inter phase 1?
Chromatin is not visible
DNA and proteins are replicated
What occurs in prophase 1?
- Chromosomes condense (get shorter and fatter)
- Chromosomes arrange into homologous pairs
- crossing over occurs
- centrioles move to opposite poles
What occurs in metaphase 1?
- Homologous pairs (bivalent) align on equator
- independent assortment occurs resulting in genetic variation
- pairs attachment to spindle fibres
What occurs in anaphase 1?
- spindles contract
- homologous pairs separate
- one chromosome from each pair moves to each side of cell
What occurs in telophase 1?
- Nuclear envelope forms
* cells formed have 2 chromosomes
What occurs in cytokinesis?
Cytoplasm divides
2 haploid daughter cells produced
What are the phases of the second mitotic division?
Interphase 2 Prophase 2 Metaphase 2 Anaphase 2 Telophase 2
What occurs in interphase 2?
Shorter
No DNA replication
Chromosomes remain visible
What occurs in prophase 2?
Centrioles replicate and move to new poles
Chromosomes condense
Nuclear envelope breaks down
Spindle forms
What occurs in metaphase 2?
Chromosomes align on equator
Independent assortment
Crossing over
What occurs in anaphase 2?
Centromeres split
Chromatids separate
What occurs in telophase 2?
4 haploid cells each with 2 chromatids produced (1 from each parent)
What is crossing over?
Homologous pairs of chromosomes come together. Chromatids twist around each other and bits of chromatids swap. Resulting in different combinations of alleles
What are the 2 processes resulting in genetic variation in meiosis?
Crossing over
Independent assortment
What happens in independent assortment?
Homologous chromosomes contain one from the father and one from the mother
When they align (m1) and separate (a1) it is completely random which chromosome ends up in each daughter cell
What does independent assortment lead to?
4 daughter dells having completely different combinations of maternal and paternal chromosomes
What does meiosis do?
Produces gametes for sexual reproduction
